Method for improved pulping using an environmentally friendly pulping aid

ABSTRACT

A safe and environmentally friendly pulping aid comprising a mixture of natural terpene-based chemicals and a dispersant blend. The pulping aid is used in the pulping of lignocellulosic biomass to simultaneously increase screened pulp yield and reduce the extractives content of pulp. The flash point of the pulping aid is at least 49° C.

FIELD OF THE INVENTION

The present invention relates to a method of improving the digestion of lignocellulose biomass used in the production of pulp, paper and paperboard products through the addition of a novel environmentally friendly pulping aid. The present invention also relates to a method of improving the production of pulp, paper and paperboard products by the addition of a novel environmentally friendly pulping aid.

BACKGROUND OF THE INVENTION

The pulping of lignocellulosic materials is well known. As described by Smook (2002, pp. 67-84), there are many pulping processes available. The pulping process of highest commercial relevance is the kraft process. Briefly described, in the kraft pulping process lignocellulosic material, typically in the form of wood chips of specified dimensions, is contacted with the “cooking liquor,” which is an aqueous mixture of pulping chemicals, principally sodium hydroxide and sodium sulfide. These chemicals, in combination with temperature, pressure and time, act to break the chemical bonds between lignin, hemicellulose and cellulose, and thus liberate cellulose fibers from the lignocellulosic matrix.

In a typical kraft process, wood chips, a common form of lignocellulosic biomass, in contact with pulping chemicals are “cooked” for a period of up to 3.5 hours or more at a temperature of about 170° C. in a large pressurized vessel or digester. In one common variation of the pulping process, at the completion of the cook, the contents of the digester are discharged into a blow tank, wherein volatile vapors are collected and where the softened chips are allowed to disintegrate into fibers and form a slurry. Heat may also be recovered during this step. Additional processing steps usually follow including: the screening of the pulp slurry to remove uncooked or partially cooked wood chips (otherwise known as “rejects”); the washing of the fibers within the pulp slurry to remove residual pulping chemicals and cook by-products such as solubilized forms of lignin degradation products; and the collection and recovery of valuable residual pulping chemicals. In the production of industrial papers, such as containerboard, the washed usually brown pulp is directed to the papermachine where it is formed into a final paper product. In the production of bleached pulp, printing papers, hygienic products, and the like, the brown pulp is bleached with a combination of bleaching chemicals, such as oxygen, ozone, chlorine dioxide and hydrogen peroxide, to achieve a specific whiteness and brightness. Smook (2002, pp. 164-181) describes the variety of pulp bleaching methods that are typically used in the production of bleached pulp.

It is widely known to those skilled in the art that the addition of certain chemicals or “pulping aids” can provide benefits to the pulping process. Pulping aids are typically added directly to the pulping chemicals and thus require little-to-no additional capital investment in new pulping equipment that would otherwise limit their use. An ideal pulping aid will increase the reactivity between the lignocellulose and the pulping chemicals. Under certain conditions, higher reactivity is desirable as it allows increased throughput and production levels and/or reduced bleaching costs. An ideal pulping aid will also eliminate or reduce unwanted effects of the pulping process. For example, wood species contain varying amounts of extractives or resinous materials that can agglomerate and form unwanted deposits or pitch within the papermaking process. Pitch deposits are objectionable, as they are not easily removed from the pulp. If these pitch deposits are not removed from the pulp they will be carried over to the final pulp or paper product, which can result in costly quality-related losses. Further, they will contaminate the surfaces on pulp and papermaking equipment, which will reduce operational efficiencies as, for example, when production must be interrupted to clean these surfaces.

Brogdon and Adiwinata (2011) describe a number of methods that have been developed to reduce pitch deposits including the addition of materials and chemicals such as adsorptive minerals like bentonite and talc; sodium thiosulphate as a de-tackifying agent; and a variety of dispersants and emulsifying agents such as papermaker's alum (aluminum sulfate). Methods for enzymatic degradation of pitch and pitch precursors using lipases and other enzymes (U.S. Pat. No. 5,176,796) have been developed but are not widely practiced due to the relatively high cost of enzymes. More recently, the addition of novel and most likely expensive inorganic materials, such as chemically modified zeolites (U.S. patent application Ser. No. 14/450,298) and precipitated calcium carbonate (U.S. patent application Ser. No. 15/129,524), have been proposed.

Of the many pulping aids that are available, anthraquinone (AQ) is one well-known example. As first described in U.S. Pat. No. 4,012,280, AQ promotes the delignification of lignocellulose by inhibiting condensation reactions between intermediates formed during pulping and the fiber. Another well-known example of a pulping aid is the use of surfactants such as ethoxylated alkyl phenols. As described in U.S. Pat. No. 4,673,460, surfactants lower the surface tension of the cooking liquor and thus promote wetting with the hydrophobic components of the wood chips. Surfactants allow reacted surface constituents of the wood chip to diffuse into the bulk thus exposing new reactive surfaces to the cooking liquor. As a result, the rate of delignification is increased. Surfactants can also partly solubilize wood resins or pitch thus reducing unwanted pitch deposit formation. However, surfactants also promote foam formation. Foam is generally regarded as a problem in most pulp and paper operations. For example, foam will impede the dewatering of the pulp slurry, resulting in operational inefficiencies, especially during pulp washing and papermaking. To control foam formation, pulp and paper producers will use defoaming agents, such as silicone-based emulsions (Spence, 1997). These defoamers are typically added in the fiber line at the brown stock washing and pulp bleaching unit operations. The addition of defoamer adds cost and can result in unwanted deposits on both papermaking equipment and in the final pulp or paper product. Yet another well-known example is the use of solvents such as the addition of kerosene as disclosed in U.S. Pat. No. 2,144,756, wherein pitch is first dissolved by an organic solvent then emulsified in situ to be removed by subsequent pulp washing steps. As discussed by Thomas (2011), the use of solvents, such as aliphatic hydrocarbons, are effective for removing organic deposits on papermachine surfaces but are currently not used because of their low flash points and their potential of generating high levels of volatile organic carbon (VOC) compounds. The flash point is the lowest temperature at which vapors of the chemical will ignite given the presence of an ignition source. Pulping aids with low flash points are not desirable because they pose environmental and safety hazards. Alternatives to petroleum-derived solvents, such as terpenes, are well-known. Terpenes are derived from natural sources and as such are biodegradable (U.S. Pat. No. 5,720,825). However, pure terpenes generally have low flash points and are thus not suitable to pulp and papermaking applications. For example, the cyclic terpene α-pinene has a reported closed cup flash point of 91° F. or 33° C. (PubChem Database).

It is well-known that terpenes are excellent cleaning agents. For example, U.S. Pat. No. 5,863,385 discloses the effectiveness of oil-in-water emulsions made from hydrocarbons, fatty alcohols, terpenes and other non-polar agents as general cleaning agents. U.S. Pat. No. 6,890,405 discloses the use of d-limonene as an effective detackifier for papermachines that produce recycled paper. However, no terpene-based pulping aid has been used in the pulping processes.

Many pulping aids have been shown to be environmentally unfriendly and/or pose safety risks. As described in U.S. Pat. No. 8,025,762, the disposal of some pulping aids is difficult, which limits their adoption. Moreover, many pulping aids, such as AQ, have been identified as carcinogens and have been discontinued in many jurisdictions (Hart and Rudie, 2014). Ethoxylated alkyl phenol degradation products have also been identified as being highly toxic to aquatic organisms, and organic solvents such as kerosene have long been discontinued due to their toxicity and flammability (Brogdon and Adiwinata, 2011). These chemicals exhibit toxicity to aquatic organisms at relatively low concentrations and must be removed from mill effluents before entering receiving waters (Borchardt et al. 1998). In contrast, Borchardt et al. have shown that linear (non-phenolic) alcohol-based surfactants biodegrade rapidly to produce non-toxic degradation products.

These examples underscore the need for a relatively low-cost, safe, environmentally friendly pulping aid that can improve the pulping process, enhance black liquor combustion, reduce and most probably eliminate the use of defoamers, as well as pitch control surfactants that can adversely affect papermachine runnability. This pulping aid would ideally increase the reactivity between lignocellulosic biomass and the cooking liquor and remove unwanted extractives that lead to pitch deposits. In doing so, the pulping aid would increase the screened yield in the production of pulp from wood and reduce or eliminate deposits that negatively influence pulping operations and the quality attributes of the final product.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved method for pulping lignocellulosic biomass through the addition of a safe and environmentally friendly pulping aid composed of a terpene mixture and a dispersant blend, which comprises a surfactant-based dispersant and a silicone-free defoamer. The combination of these materials has led to the discovery of a pulping aid that simultaneously improves screened pulp yield and reduces the extractives content of the pulp, thus reducing or eliminating the deposition of extractive-containing pitch. The pulping aid is safe, biodegradable and thus environmentally friendly. The terpene component of the pulping aid is ideally derived from a class of natural products, namely cyclic terpenoids and the like, including the citrus by-product, d-limonene. The pulping aid is added to the pulping process, either in the pretreatment of the lignocellulosic biomass or during digestion or both. The pulping aid is designed to have a high flash point of at least 49° C. to 93° C. and preferably at least 60° C. to 77° C. to ensure safe storage and handling, and to minimize the release of harmful VOCs. Not to be bound by any specific mechanism or mode of action, the pulping aid is thought to act on pitch-generating molecules or particles, especially those formed from the saponifiable (fatty and resin acids) as well as the unsaponifiable (neutrals) components released from lignocellulosic biomass, such that they can be removed during subsequent pulping operations, namely pulp washing. The removal of pitch-forming chemicals from lignocelluslosic biomass makes it more accessible to the pulping chemicals, which leads to enhanced pulping characteristics. Further, the addition of the pulping aid results in a beneficial reduction in the extractives content of the pulp.

It is an object of the present invention to provide an improved method for pulping wherein the amount of pitch-generating components present in the pulp is reduced to improve the efficiency of pulping processes used to produce kraft, sulfite, and soda-based pulps, and dissolving pulps.

It is a further object of the present invention to provide an additive that increases the efficiency of the pulping process by increasing the screened pulp yield.

It is a still further object of the present invention to provide an additive for the pulping process that reduces and most probably eliminates the need to use other additives such as silicone-based defoamers, dispersants, talc and the like.

It is a still further object of the present invention to provide an additive for the pulping process that enhances the papermachine runnability by reducing or eliminating foam without the use of defoamers added in the fiber line.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a typical batch pulping process that will be used to illustrate the typical addition points of the pulping aid. It should be understood by those skilled in the art that pulp mills with continuous digesters can equally benefit from this invention. Lignocellulosic biomass, such as wood chips, are transferred to a digester (1) in which they may be subjected to a pretreatment such as preheating of the wood chips by steam or pre-impregnation of the wood chips by pulping chemicals. The wood chips are then contacted by the pulping chemicals, heated to the pulping temperature, and allowed to delignify or cook. Following the digestion step, the contents of the digesters are transferred to the blow tank (2). Typically, this is accomplished by a release of pressure from the digester to the blow tank, which is at or near atmospheric pressure. During the discharge of the blow tank, volatile low-molecular weight chemicals are flashed off and recovered. The contents in the blow tank are held for a period of time to allow wood chips to defiberize completely into a pulp slurry of relatively high consistency (solids content). Wood chips that are partially defiberized or not defiberized are rejected at screening elements or knotters (3). These rejects are often repulped, landfilled, or combusted for their heating value. The pulp slurry is then washed in pulp washers (4) to remove residual pulping chemicals, solubilized lignin and other pulping by-products, including solubilized extractives. The washed pulp may then be directed to the papermaking process in the case of containerboard production and the like or to the bleach plant for bleaching and removal of chromophores that give unbleached pulp its brown color and achieve the pulp's target whiteness and brightness.

DETAILED DESCRIPTION OF THE INVENTION

According to one aspect of the present invention, there is provided an improvement in a pulping process whereby lignocellulosic biomass is contacted by a pulping aid of this invention comprising a terpene or a blend of terpene fractions derived from natural sources such as plants, fruits and vegetables or trees to the cooking liquor, the terpene being added in an amount of at least 0.2 lb to 10 lbs per ton (2,000 lbs) of dry wood chips.

The pulping aid of the present invention may be utilized in a chemical pulping process. As kraft is the most widely used process, reference will be made to this process with the understanding that one may also use the pulping aid in the sulfite process or other aqueous-based pulping processes, including those processes used in the production of dissolving pulps. With reference to FIG. 1, the preferred addition points in the pulping process are either at a pretreatment stage (in the case of mills with continuous digesters) or at the digester (1) (in the case of mills with either batch or continuous digesters). It will be recognized that in an efficient recovery process either the terpene or terpene blends will be recovered in the blow tank (2), washers (4), and from recirculated process flows. The recovered terpene or terpene blends can be isolated as a by-product or used as a fuel for their heating value.

As a natural product, the terpenes and their selected fractions utilized in the present invention may be derived from a variety of sources including: plants, camphor, conifers, orange or lemon peels, as well as the sulphite process and/or the kraft process. Although some insects produce terpenes, they are not a major source thereof. It should be recognized that other suitable sources are available such as terpenes derived from the destructive distillation of rubber. Preferably, the terpenes used in the present invention are selected from one or more of the following terpenes: α-pinene, β-pinene, camphene, 3-carene, l-limonene, d-limonene, m-cymene, p-cymene, α-terpineol, α-phellandrene and β-phellandrene and derivatives thereof.

It is preferred that the terpenes be used in combination with an environmentally friendly dispersant blend. The dispersant blend will be between 3% and 90% by weight of the final formula. The preferred dispersant blend is composed of one non-phenolic alcohol ethoxylate selected from the following: decyl alcohol ethoxylate, dodecyl alcohol ethoxylate, and tridecyl alcohol ethoxylate. The ethoxylated alcohols act as wetting agents and are selected in part on their hydrophilic-lipophilic balance (HLB), which is typically between 13 and 14. Additionally, the dispersant blend includes preferably one silicone-free defoamer selected from the group of difunctional block copolymers based on ethylene oxide and propylene oxide and having a hydrophilic-lipophilic balance (HLB), typically between 3 and 4. The amount of silicone-free defoamer will generally be between 1% and 10% by weight of the dispersant blend. The dispersant blend is nontoxic, silicone-free and readily biodegradable.

The volume of pulping aid added to the cooking liquor may vary widely depending on the wood species being pulped or their blends. Thus, while a certain amount of the pulping aid will give improved results, it will be understood that larger or smaller amounts may be used with the result varying accordingly. It will be further understood that the amount to add will be a question that is answered by providing the optimum amount needed to provide improved pulp properties cost effectively.

The volume added will further depend upon the particular terpene or mixture of terpenes added to the cooking liquor, which may vary depending on market prices. Thus, many different terpenes are available as a mixture thereof and the amount added to the pulping process will depend upon the particular make up of that mixture. It suffices to say that one skilled in the art could determine the ideal amount with appropriate experimentation.

Generally, the amount of pulping aid added to the digester will be at least 0.2 lbs to 10 lb per ton (2,000 lbs) of dry wood chips. It has been found that with many terpenes, this level of addition provides an improvement and at 0.5 lb per ton to 2.5 lb per ton of dry pulp, a substantial improvement in the pulping process is observed.

To illustrate the benefits of the present invention three pulping trials were conducted at a kraft pulp mill using standard kraft cooks with cooking temperatures around 170° C. In all cases, the pulping aid was introduced in the digester at a dosage level of between 0.2 lbs to 10.0 lbs per ton of wood chips (on an oven dry basis). The total contact time between the pulping aid and the wood chips was approximately 3.5 hours. Three wood chip types or blends were considered. H-factor, rejects and pulp extractives content were used to measure the impact of the pulping aid addition of this invention. It will be apparent to those skilled in the art that H-factor is an important dimensionless kinetic factor describing the impact of time and temperature on the rate of delignification. In general, a lower H-factor is desirable as the process throughput is increased as the H-factor is lowered. Rejects are wood chips that are partially defiberized or not defiberized and removed by the knotters (3). It will be apparent to those skilled in the art that a lower level of rejects is preferred as the overall screened pulp yield is increased as rejects are lowered. Extractives will be recognized as the dichloromethane-extractable content of pulp, which represents a measure of such substances as waxes, fats, resins, sterols and non-volatile hydrocarbons as described by TAPPI Standard Method T 204 cm-97. All results were compared to a control.

The following examples illustrate various aspects of the invention but are not to be interpreted as limiting it. These examples are merely representative and are not inclusive of all of the possible embodiments of the invention. Results are summarized in Table 1.

Example 1

A multi-day trial was used to determine the impact of the pulping aid of this invention on mill pulp production. Hardwood chips comprising a majority of maple wood chips were contacted with between 0.2 lbs and 4.0 lbs of pulping aid per ton of dry pulp, the pulping aid being a mixture of 60% terpenes and 40% of a dispersant blend. As summarized in Table 1, at a constant addition level of 2.5 lbs per dry ton of pulp, the H-factor was unchanged. However, rejects were reduced by 45% and the pulp extractives content was reduced by 57.3%. The incremental fiber production realized from the lower rejects level was about 14.4 dry tons per day. Furthermore, the use of a surfactant-based pitch control chemical was eliminated and the use of defoamers was reduced by about 20%.

Example 2

A multi-day trial was used to determine the impact of the pulping aid of this invention on mill pulp production. Hardwood chips comprising a majority of aspen wood chips were contacted with between 0.2 lbs and 4.0 lbs of pulping aid per ton of dry pulp, the pulping aid being a mixture of 60% terpenes and 40% of a dispersant blend. As summarized in Table 1, at a constant addition level of 2.5 lbs per dry ton of pulp, the H-factor was reduced by 8.0%; rejects were reduced by 53% and the pulp extractives content was reduced by 27.3%. In addition, the pulp production rate of the mill was increased by 4.4% from the base rate. The incremental fiber production realized from the lower rejects level was 7.5 dry tons per day. Furthermore, the use of a surfactant-based pitch control chemical was eliminated and the use of defoamers was reduced by about 20%.

Example 3

A relatively long (multi-week) trial was used to determine the robustness of the method of this invention on mill pulp production. Hardwood chips comprising a blend of aspen and maple wood chips were contacted with 0.2 lbs and 4.0 lbs of pulping aid per ton of dry pulp, the pulping aid being a mixture of 60% terpenes and 40% of a dispersant blend. As summarized in Table 1, at a constant addition level of 0.5 lbs per dry ton of pulp the H-factor was reduced by 6.7%; alkalinity was reduced by 4.3% from 23.0 g/L; rejects were reduced by 47% and the pulp extractives content was reduced by 36.1%. Further, the pulp production rate of mill was increased by 4.8% from the base rate. The incremental pulp fiber production realized from the lower rejects level was 5.5 dry tons per day. Furthermore, the use of a surfactant-based pitch control chemical was eliminated and the use of defoamers was reduced by about 20%.

TABLE 1 H-Factor Extractives (g/L) Rejects Percent Percent Incremental Tons Example Baseline Change Baseline Change per Day as Pulp 1 350  0.0% 0.10 −57.3% 14.4 2 275 −8.0% 0.15 −27.3%  7.5 3 350 −6.7% 0.10 −36.1%  5.5

In summary, benefits observed during the trial periods included a reduction in knotter rejects, a reduction in pitch deposits, the ability to reduce pitch control chemical addition, the ability to decrease defoamer in the fiber line, and the ability to lower cooking liquor alkalinity, at reduced H-Factor, while achieving brown stock kappa number targets.

LIST OF REFERENCES

-   U.S. Pat. No. 2,144,756 -   U.S. Pat. No. 4,012,280 -   U.S. Pat. No. 4,673,460 -   U.S. Pat. No. 5,176,796 -   U.S. Pat. No. 5,720,825 -   U.S. Pat. No. 6,890,405 -   U.S. Pat. No. 8,025,762 -   U.S. patent application Ser. No. 14/450,298 -   U.S. patent application Ser. No. 15/129,524

NON PATENT LITERATURE

Borchardt, J. K., Cano, M. L., Tortorici, P. L., Wallace, J. C., Kravetz, L., Guin, K. F., and Dubey, S. T., “Environmental Aspects of Alcohol Ethoxylates in Pulp and Paper Mills. Part 1 Surfactant Chemical Structure Effects,” 1998 Environmental Conference Proceedings, TAPPI Press, 1998.

Brogdon, Brian N. and John Adiwinata, “A Review of Deresinators as Digester Additives for Kraft Pulping,” TAPPI 2011 PEERS Conference, TAPPI Press, October 2011, pp. 935-961.

Hart, Peter W. and Alan W. Rudie, “Anthraquinone-A Review of the Rise and Fall of a Pulping Catalyst,” TAPPI Journal, 13(10), 23-31, 2014.

National Center for Biotechnology Information. PubChem Compound Database; CID=6654, https://pubchem.ncbi.nlm.nih.gov/compound/6654 (accessed Dec. 31, 2017).

Smook, Gary A., “Handbook for Pulp & Paper Technologists,” 3^(rd) ed., Angus Wilde Publications, 2002.

Spence, Gavin G., “Defoamers for Brown Stock Washers,” TAPPI 1997 Pulping Conference Proceedings, TAPPI Press, 1997.

Thomas, George S., “Agricultural Based Solvent Cleaners for the Pulp and Paper Industry,” TAPPI PaperCon'09 Conference, June 2009.

T 204 cm-97, “Solvent extractives of wood and pulp,” TAPPI Press, 1997. 

I claim:
 1. A safe and environmentally friendly pulping aid comprising a mixture of at least one terpene and a dispersant blend.
 2. The pulping aid according to claim 1 wherein the terpene mixture is selected from but not limited to one or more of the following biodegradable terpenes: α-pinene, β-pinene, camphene, 3-carene, l-limonene, d-limonene, o-cymene, m-cymene, p-cymene, α-terpineol, α-phellandrene and β-phellandrene, α-terpinolene, α-terpinene and β-terpinene.
 3. The pulping aid according to claim 1 wherein the dispersant blend is a non-phenolic, readily biodegradable alcohol ethoxylate selected from but not limited to the following: decyl alcohol ethoxylate, dodecyl alcohol ethoxylate, and tridecyl alcohol ethoxylate, and one or more defoamers selected from but not limited to the group of difunctional block copolymers based on ethylene oxide and propylene oxide.
 4. The pulping aid according to claim 1 wherein the terpene content has a range between 10% and 97%.
 5. The pulping aid according to claim 1 wherein the dispersant blend has a range between 3% and 90%.
 6. The pulping aid according to claim 1, wherein the closed cup flashpoint is at least 49° C.
 7. A method of using an environmentally friendly pulping aid containing a mixture of at least one terpene and a dispersant blend is brought into contact with lignocellulosic biomass during the pulping process.
 8. The method according to claim 7 where the pulping process is a kraft pulping process.
 9. The method according to claim 7 where the pulping process is a sulfite pulping process.
 10. The method according to claim 7 where the pulping process is soda pulping process.
 11. The method according to claim 7 where the pulping additive is brought into contact with lignocellulosic biomass during the pretreatment stage.
 12. The method according to claim 7 where the pulping additive is brought into contact with lignocellulosic biomass during the digestion stage.
 13. The method according to claim 7 where the pulping additive is brought into contact with lignocellulosic biomass in both the pretreatment and digestion stages.
 14. The method according to claim 7 where the contact time between the pulping aid and the lignocellulosic biomass during pulping is at least 2 hours and the pulping temperature is at least 130° C. in the case of sulphite pulping and at least 160° C. in the case of kraft pulping.
 15. The method according to claim 7 where the addition level of the pulping additive is between 0.2 lbs and 4.0 lbs per ton of dry pulp.
 16. A pulp product derived from lignocellulosic biomass produced using a safe and environmentally friendly pulping aid comprising a mixture of at least one terpene and a dispersant blend where the extractives content of the unbleached pulp is reduced by at least 25%.
 17. A pulping process employing a safe and environmentally friendly pulping aid comprising a mixture of at least one terpene and a dispersant blend where at the same brownstock kappa number target as the control, the rejects are reduced by at least 45%, the pulp production is increased by at least 4.0%, the surfactant-based pitch control chemical is eliminated and the use of defoamers in the fiber line is reduced by at least 20%. 